Variable oscillator for code practice (CB7317E)

This circuit is from Popular Electronics from the 90s. The integrated circuit is not very common nowadays.

Voltage controlled oscillator (CB20605E)
This VCO makes use of components from the 1980s. The circuit can be implemented with modern...
Ambient light indicator (CB21567E)
This circuit uses an LDR as a sensor to trigger an LED indicator at a preset lighting level. The...
High Impedance 2 W Amplifier (CB6163E)
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...